1. Technical Field
This invention relates to a counter assembly for use in conjunction with a fluid meter to provide flow volume information corrected to a standard. In particular, the invention is concerned with an improvement in a mechanical computer arrangement contained within the counter assembly to provide for the correction of a measure of actual flow.
2. Background Information
Typically, meters used to measure the flow of gases, such as natural gas, measure in quantities of cubic feet. With natural gas being sold on a cubic foot basis it is important both from the supplier's standpoint and the consumer's standpoint that the heating value of each cubic foot purchased be constant. However, the heating value of a cubic foot of natural gas changes dependent upon both temperature and pressure. As a result, measured quantities of gas are corrected to standard cubic feet. A standard cubic foot is representative of that amount of gas which occupies a cubic foot of space at a standard temperature and pressure. Under normal service conditions, changes in the temperature of the gas are more dramatic and likely to have a much greater effect upon the correction to standard than are the changes in the pressure of the gas.
To provide for corrections due to temperature, gas meters include counters with mechanical computers which correct measured volumes of gas flow to standard. Generally, the way in which this is done is to convert the constant directional rotational motion of the meter rotors into oscillating arcuate motion and then to change the length of the arc based upon the difference in temperature from standard. A more detailed description of one form of counter employing the foregoing principle is described in U.S. Pat. No. 3,581,566.
Another arrangement utilizing the foregoing principle is disclosed in U.S. Pat. No. 3,969,939. As disclosed in this latter patent, the rotational motion of the output of the constant displacement rotors of the meter is converted by means of a crank wheel and lever link into an oscillating arcuate motion of a radial arm. An outer end of the arm, thus swings along an arcuate path. Positioned within the path is a cam surface whose location controls the length of the arc through which the end of the arm swings. The location of the cam surface within the path changes dependent upon temperature. The arm itself is attached to the input hub of a one way clutch so that, when the end of the arm swings from a start position most distant from the cam surface toward the cam surface no motion is transmitted through the hub to an output shaft connected to a register. However, when the arm swings away from the cam surface, back toward its start position the input hub couples with the output shaft so the two rotate together. The amount of rotation of the output shaft represents a gas flow volume through the meter corrected for temperature. When further movement of the link is halted by the outer end of the arm engaging the cam surface, a lost motion spring connection between the crank wheel and the link allows the crank to slide within the link.
At standard temperature, the distance travelled by the outer end of the arm is a standard length measured from its initial position most distant from the cam surface to the standard temperature point on the cam surface. As the temperature of the gas flowing through the meter changes either up or down from standard, a corresponding change occurs in the location of the cam surface intersecting the path of the arc of travel of the arm. At the cam end of the arc, the length is either increased or decreased. At the start of each oscillation, the computer arm is returned to the same initial end position of the arc. If when starting each oscillation, the outer end of the computer arm is not in registry with the initial position of the arc, an erroneous measure of gas volume will be obtained because the length travelled by the arm will be incorrect for the cam surface temperature setting which intersects the arc. The ability to adjust the position of this starting point is therefore important to the accuracy of the meter.
In the meter disclosed in U.S. Pat. No. 3,969,939, adjustment of the initial end position of the arc of travel for the outer end of the radial arm is achieved by using a set screw to change the end position of the slot in the link. Adjustment of the set screw requires interruption in the operation of the meter owing to the virtually continuous motion of the link which carries the set screw.
In U.S. Pat. No. 3,581,566, adjustment of the start end position of the arc travelled by the computer arm is achieved by adjustment of the set screw carried on the driven arm and engaged by a portion of a driving arm. In this arrangement, the latter is oscillated about an idler bearing by reciprocation of a connecting rod to a crank driven through a gear train connected with the meter rotors.